Your forefinger should be able to fit in between your collar and your neck when the shirt is buttoned to the top.
The collar's tips and outer edge should be covered by your blazer or suit jacket's lapels. To ensure that this happens, always fit your dress shirts and button-downs before fitting your jackets and blazers.
Looking for a full cut shirt with more room to move - try Van Heusen Classic fit. For a more relaxed yet tailored look try our Van Heusen European or for a slim silhouette look for Van Heusen Slim.